MIMO wireless communication systems comprise multiple-antenna wireless communication devices on both ends of a communication link, e.g., at a base station (BS) and a mobile station (MS). MIMO wireless communication techniques can enhance the radio link reliability and increase the system capacity through diversity gain and multiple signal stream transmission. Beamformed MIMO schemes have demonstrated significant benefits for MIMO systems. Through proper beamforming, the channel condition of a MIMO channel matrix can be improved and the signal strength of all the signal streams to be transmitted from one device to the other can be increased.
In a beamforming MIMO system, the BS transmits up to K=min(M,N) data streams simultaneously, where M is the number of antennas at the BS and N is the number of antennas at the MS. In this way, the BS assigns to the MS up to K beams, or beam patterns that are associated with the channel condition between the BS and a particular MS. The beamforming weight vectors needed to achieve the best beam patterns can be computed when spatial signature information between the antennas of the BS and the antennas of the particular MS is known.
Hybrid automatic repeat request (HARQ) transmission techniques are used in wireless communication systems when an original transmission is not received by the destination device. In one variation of a HARQ technique, the same original message is retransmitted when necessary, and the receiver combines the retransmitted message with the previously received original message in order to decode the original message. Another HARQ technique is called “incremental redundancy” and involves transmission of only a portion of the original message, and more specifically, a different portion of the original message at each retransmission attempt.
Techniques are provided herein to improve the performance of any type of HARQ retransmission scheme in a MIMO wireless communication system.